Refining zinciferous lead



Dec. 3, 1946. w. w. SHROPSHIRE 'REFINING ZINCIFEYROUS LEAD Filed De c. 22, 1943 ATTORNEYS Patented Dec. 3, 1946 UNIT-ED STATES PATEN T OFFICE nEFiNii IdZINoIFERoUs LEAD William Wallace Shropshire; Chicago,'lll., assignor to International Smelting'& Refining Company, New York,'N. Y., a cor'poration' of Montana " A plication December 22, is isQseriallvo;515,221

This invention relates to the refining treme ject the provision 'of certain improvements in the process of refining zinciferous lead with'chlorine.

In desilverizing argentiferous leadby the Parlses process, the desilverized lead contains upwards to 0.55% zinc. This zinc must be removed to render the lead salable. While several methods are known and practiced for dezincing such zinciferous lead, the present invention is primarily concerned with the process in which the zinc is removed by the preferential action of chlorine on zinc when the chlorine is brought into contact with 'a mixture of lead and zinc in the molten state. As is well known in the art, chlorine reacts preferentially with zinc as long as any zinc is present in the molten metal, in accordance with the following reaction:

ZI1+C12 ZllC 12 If and when the zinc has beenpractically allgremoved and chlorine remains in contact with the dezinced lead, the following reaction will take place:

c Pb+Clz PbCl2 While this reactionand the resultant formation of lead chloride is not desirable, in practice it is permittedto take place in order to completely dezinc the lead at a satisfactoryrate, nd consequently some lead chloride is produced with and ride product, so that the contaminated product 'must be purified before it can be sold as zinc chloride.

The processes and apparatusheretofore com- I monl'y used for dezincing zinciferous lead produce a zinc chloride-slag or product contaminated with 'lead chloride.

I Furthermore, no entirely satisfactory method is available for separating or removing the slag of mixed zinc and lead chlorides from thejsurface of the molten refined'lead except by laborious skimming or ladling. Thismethod of handling the slag is costly, and taken. with the cost ofthe subsequent purification of the slag,

so'increases the cost of the dezincing treatment as to frequently render it of doubtful economy. The present invention aims to overcome the I foregoing objectionable and costly features in the snemteioreaqleepalt a aet edmsteesls .Qf 'nnaagzmcrrerous lead by theaction of chlorine.

" 5 Claims. (01. 75 '78) I have discovered that it is possible torefinejthe zinciferous lead with chlorine, purify the resulting zinc chloride slag, and separate thepurified 'zinc chloride' from the refined lead in substantially one operation. Based on this discovery, the

present invention involves an improved process of refining zinciferous lead by the action of chlorine.

In accordance with the method of the invention,

chlorine is introduced at spaced intervals'of the length of an elongated bath of molten zinciferous lead of progressively decreasing zinc content and thereby there is formed on t f QSI-Irfacefof the molten metal a molten slag of mixed zinc and lead chlorides of progressively decreasing lead chloride content in the direction of the progressively increasing zinc content of the molten metal bath. Molten lead (preferably substantially zinc-free) is withdrawn from the molten metal bath approximate the end of its minimum zinc content, and

"zinc chloride (preferably substantially free from lead chloridelis'withdrawn from'the' bath approximate its other end. The operation is preferably carried out in a continuous'manner by continuously supplying molten zinciferous lead to 1 that end of the elongated bath of maximum zinc content, continuously withdrawing molten lead (preferably substantially zinc-free) from the other end of the bath, and continuously withdrawing molten zinc chloride (preferably substantially free of lead chloride) from the bath approximate the supply of zinciferous lead there'- to and at a level above the level of the bath.

The invention ,will be better understood from the following description taken in conjunction with the accompanying drawing showing appacomprises a rectangular container or tank 5open at the top, but covered, in operation, with a suitable hood 6 (Fig.3). The container is divided into two compartments! and 8 by a centrally positioned longitudinal partition 9. The height of the partition 9 corresponds substantially with the depth of the container 5. one end of the partition fits snugly against the'adjacentjend ne? ename an wea he and .9; the. imt'it'ion is'provided with two-openings l0 'and. H

at different levels. The opening I is at or near the bottom of the container, while the opening H is near the top of the container, and the two openings thus permit communication between the two compartments 1 and 8 near the bottom and top thereof, respectively. .The two communicating compartments I and 8 form an elongated treatment zone having an effective length about twice the length of the container.

The compartment '1 of the container has a transverse baffle I2 near the end opposite the openings [0 and H of the partition 9. The baflle l2 depends from the top of the container to within a short distance of the bottom, thereby providing a space beneath the battle for the flow of molten metal. The compartment 8 has, at the same end, a similar transverse and depending baflle I3, although the bafile I3 is somewhat nearer the end of the container than is the baflie l2.

An external (slag-discharge) well i4 is provided adjacent the compartment 1 and slightly further from the end of the container than the bafile I2. Communication between the compartment 1 and the well I4 is provided by two openings l5 and I6 at different levels in the side wall of the container (Fig. 3). The well M has a discharge outlet I! at about the same level as the upper opening Hi.

The baflie I2, forms,.in effect, a charging well 18 communicating (beneath the baflle 12) with the compartment 1. Molten metal is supplied to the charging well l8 from a delivery pipe l9. The baffle l3 forms, in effect, a discharging well 20 at the same end of the container, in communication (beneath the baflle I3) with the compartment 8. The discharge well 26 has an outlet 2l at approximately the same level as the lower edge of the opening II, and slightly lower than the upper opening [6 into the slag-discharge well It. An outlet 22 communicating with the bottom of the compartment 8 is provided for emptying the container.

Pipes 23 having valves 24 depend from a header 25 into the compartments 1 and 8 at spaced intervals in the length thereof. These pipes, when practicing the method of the invention, serve to supply chlorine to the molten lead, and it will be noted that a substantial distance separates the (slag-discharge) well l4 and the nearest chlorine delivery pipe 23.

In practicing the method of the invention in the apparatus illustrated in the drawing, molten zinciferous lead is delivered from the pipe i9 to the charging well 18 communicating with the compartment 1. The molten metal may be derived from any suitable source, such as a furnace, kettle or the like, and may be supplied to the delivery pipe 19 in any appropriate manner. The molten metal flows under the bafile 52, through compartment 1, through opening it] into compartment 8, under bafiie 13 into the discharging well 26 and rises to the level of the overflow or outlet pipe 2|. The overflow pipe 2| controls the level of the bath of molten lead in compartments 1 and 8, and the lower edge of the opening ll (adjustable if desired) is at approximately the level of the molten lead bath. Molten metal is delivered to the charging well IS in a continuous stream, and, after filling the container to the level controlled by the overflow pipe 2|, is conducted back to a molten metal reservoir.

Chlorine gas is introduced into the molten metal bath through the pipes 23, the rate of 4 chlorine delivery of each pipe being capable of individual adjustment through the valves 24. With molten metal flowing or circulating through the container, chlorine in controlled amount is allowed to pass through the pipes 23 into the moving elongated stream or bath of molten metal. The chlorine reacts with the :zinc and some lead to form a molten slag of mixed zinc and lead chlorides which rises to the surface and floats on the molten metal. Battle l3 traps the molten slag on the metal discharge end of the container, and in order to leave the container the slag must rise to the level of the opening l6 of the slag-discharge well 14. Thus, as slag is continuously formed and builds up to a level slightly higher than the opening I6, a continuous flow of slag is maintained from compartment 8, through opening H (the lower edge of which is approximately coincident with the molten metal level), into compartment 1, and thence to the slag-discharge well M. The flow of the molten slag is countercurrent to the flow of the molten metal upon which it floats.

By appropriate control of the rate of impure metal delivery (through pipe l9) or of the chlorine delivery rate, or both, the metal becomes progressively lower in zinc content in the direction of its flow until it reaches the metal discharge well 20 as dezinced metal. In the final stages of dezincing, that is towards the end of the compartment 8 adjacent the metal discharge well 20, some lead chloride will be formed, and, mixed with zinc chloride, will flow towards the slag discharge well M. In the course of its flow, and more particularly towards the end of the compartment 1 adjacent the charging well l8 where the zinc content of the molten metal is highest, the lead chloride reacts with zinc to form zinc chloride and lead, in accordance with the following reaction:

Thus, the lead chloride content of the molten slag decreases in the direction of its flow, until approximate the slag discharge well M the slag is substantially free of lead chloride. In order to avoid any formation of lead chloride near the slag discharge well, no chlorine is introduced into the molten metal for some distance from the well in the direction of the molten metal flow. The relatively high zinc content of the molten metal in the vicinity of the slag discharge well insures the removal of lead chloride from the slag before it flows into the slag discharge well. From the slag discharge well M to the metal discharge well 20, the lead chloride content of the floating slag progressively increases.

The zinc chloride slag, substantially free of lead chloride, flows by gravity from the compartment 1, through the opening I6 into the slag discharge well M. The relatively quiescent condition of the molten metal and slag in this well permits any metal entrained in the slag to settle out, and to return to the compartment '1 through the lower opening l5. Since the opening I6 is at a higher level than the metal overflowpipe 2|, only slag can be discharged through the opening IS. The molten and purified zinc chloride (slag) flows by gravity-through the outlet l'l into any suitable container. It may be barreled for shipment without further treatment, or it may be discharged into water, dissolved and recovered as zinc chloride solution.

The invention permits the complete dezincing of zinciferous lead and the production and recovery of substantially pure zinc chloride in a single operation. The rate of passage of the molten metal through the container depends upon the zinc content of the metal. While I now prefer to efiect the complete dezincing of the lead with one passage through the container, it is to be understood that the molten metal may be recirculated through one container until completely dezinced, or passed consecutively through two or more containers in series. The invention results in higher and more satisfactory metal recovery, reduces labor requirements, and saves wear and tear on unnecessary equipment.

I claim:' I

1. In the process of refining zinciferous lead with chlorine, the improvement which comprises providing an elongated bath of molten lead of progressively decreasing zinc content, introducing chlorine into the bath at spaced intervals of the baths length and thereby forming on the surface of the bath a molten slag of mixed zinc and lead chlorides of progressively decreasing lead chloride content in the direction of the progressively increasing zinc content of the bath, Withdrawing molten lead from the bath approximate the end of its minimum zinc content, and withdrawing molten zinc chloride from the bath approximate its other end.

2. In the process of refining zinciferous lead with chlorine, the improvement which comprises providing an elongated and moving bath of molten lead of progressively decreasing zinc content, the movement of said bath being in the direction of its decreasing zinc content, introducing chlorine into the bath at spaced intervals of the baths length and thereby forming on the surface of the bath a moving molten slag of mixed zinc and lead chlorides of progressively decreasing lead chloride content in the direction of the progressively increasing zinc contentof the bath, the movement of the molten slag being countercurrent to the movement of the molten lead bath, withdrawing molten lead from the bath approxistantially zinc-free, and the molten zinc chloride withdrawn from the bath is substantially free from lead chloride.

4. In the process of claim 2, carrying out the refining of the zinciferous lead in a substantially continuous manner by continuously supplying molten zinciferous lead to that end of the elongated bath of maximum Zinc content and continuously withdrawing molten lead from the other end of the bath, and continuously withdrawing molten zinc chloride from the bath approximate the supply of zinciferous lead thereto and at a level above the level of the molten lead bath.

5. In the process'of refining zinciferous lead with chlorine, the improvement which comprises providing an elongated and moving bath of molten lead of progressively decreasing zinc content, the movement of said bath being maintained in the direction of its decreasing zinc content by continuously supplying molten zinciferous lead to that end of the bath of maximum zinc content and continuously withdrawing substantially zincfree molten lead from the other end of the bath, introducing chlorine into the bath at spaced intervals of the baths length and thereby forming on the surface of the bath a moving molten slag of mixed zinc and lead chlorides of progressively decreasing lead chloride content in the direction of the progressively increasing zinc content of the bath, the movement of said molten slag being countercurrent to the movement of the molten lead bath, and continuously withdrawing molten zinc chloride substantially free from lead from the bath approximate the supply of zinciferous lead thereto and at a level above the level of the molten lead bath.

WILLIAM WALLACE SI-IROPSHIRE. 

